Heavy oil and bitumen resources are supplementing the decline in the production of conventional light and medium crude oils, and production from these resources is steadily increasing. Pipelines cannot handle these crude oils unless diluents are added to decrease their viscosity and specific gravity to pipeline specifications. Alternatively, desirable properties are achieved by primary upgrading. However, diluted crudes or upgraded synthetic crudes are significantly different from conventional crude oils. As a result, bitumen blends or synthetic crudes are not easily processed in conventional fluid catalytic cracking refineries. Therefore, in either case further processing must be done in refineries configured to handle either diluted or upgraded feedstocks.
Many heavy hydrocarbon feedstocks are also characterized as comprising significant amounts of BS&W (bottom sediment and water). Such feedstocks are not suitable for transportation by pipeline, or refining due to their corrosive properties and the presence of sand and water. Typically, feedstocks characterized as having less than 0.5 wt.% BS&W are transportable by pipeline, and those comprising greater amounts of BS&W require some degree of processing or treatment to reduce the BS&W content prior to transport. Such processing may include storage to let the water and particulates settle, and heat treatment to drive off water and other components. However, these manipulations add to operating cost. There is therefore a need within the art for an efficient method of upgrading feedstock having a significant BS&W content prior to transport or further processing of the feedstock.
Heavy oils and bitumens can be upgraded using a range of processes including thermal (e.g. U.S. Pat. Nos. 4,490,234; 4,294,686; 4,161,442), hydrocracking (U.S. Pat. No. 4,252,634), visbreaking (U.S. Pat. Nos. 4,427,539; 4,569,753; 5,413,702), or catalytic cracking (U.S. Pat. Nos. 5,723,040; 5,662,868; 5,296,131; 4,985,136; 4,772,378; 4,668,378, 4,578,183) procedures. Several of these processes, such as visbreaking or catalytic cracking, utilize either inert or catalytic particulate contact materials within upflow or downflow reactors. Catalytic contact materials are for the most part zeolite based (see for example U.S. Pat. Nos. 5,723,040; 5,662,868; 5,296,131; 4,985,136; 4,772,378; 4,668,378, 4,578,183; 4,435,272; 4,263,128), while visbreaking typically utilizes inert contact material (e.g. U.S. Pat. Nos. 4,427,539; 4,569,753), carbonaceous solids (e.g. U.S. Pat. No. 5,413,702), or inert kaolin solids (e.g. U.S. Pat. No. 4,569,753).
The use of fluid catalytic cracking (FCC), or other units for the direct processing of bitumen feedstocks is known in the art. However, many compounds present within the crude feedstocks interfere with these processes by depositing on the contact material itself. These feedstock contaminants include metals such as vanadium and nickel, coke precursors such as (Conradson) carbon residues, and asphaltenes. Unless removed by combustion in a regenerator, deposits of these materials can result in poisoning and the need for premature replacement of the contact material. This is especially true for contact material employed with FCC processes, as efficient cracking and proper temperature control of the process requires contact materials comprising little or no combustible deposit materials or metals that interfere with the catalytic process.
To reduce contamination of the catalytic material within catalytic cracking units, pretreatment of the feedstock via visbreaking (U.S. Pat. Nos. 5,413,702; 4,569,753; 4,427,539), thermal (U.S. Pat. Nos. 4,252,634; 4,161,442) or other processes, typically using FCC-like reactors, operating at temperatures below that required for cracking the feedstock (e.g U.S. Pat. Nos. 4,980,045; 4,818,373 and 4,263,128;) have been suggested. These systems operate in series with FCC units and function as pre-treaters for FCC. These pretreatment processes are designed to remove contaminant materials from the feedstock, and operate under conditions that mitigate any cracking. These processes ensure that any upgrading and controlled cracking of the feedstock takes place within the FCC reactor under optimal conditions.
Several of these processes (e.g. U.S. Pat. Nos. 4,818,373; 4,427,539; 4,311,580; 4,232,514; 4,263,128) have been specifically adapted to process “resids” (i.e. feedstocks produced from the fractional distillation of a whole crude oil) and bottom fractions, in order to optimize recovery from the initial feedstock supply. The disclosed processes for the recovery of resids, or bottom fractions, are physical and involve selective vaporization or fractional distillation of the feedstock with minimal or no chemical change of the feedstock. These processes are also combined with metal removal and provide feedstocks suitable for FCC processing. The selective vaporization of the resid takes place under non-cracking conditions, without any reduction in the viscosity of the feedstock components, and ensures that cracking occurs within an FCC reactor under controlled conditions. None of these approaches disclose the upgrading of feedstock within this pretreatment (i.e. metals and coke removal) process. Other processes for the thermal treatment of feedstocks involve hydrogen addition (hydrotreating), which results in some chemical change in the feedstock.
U.S. Pat. No. 4,294,686 discloses a steam distillation process in the presence of hydrogen for the pretreatment of feedstock for FCC processing. This document also indicates that this process may also be used to reduce the viscosity of the feedstock such that the feedstock may be suitable for transport within a pipeline. However, the use of short residence time reactors to produce a transportable feedstock is not disclosed.
During processing of heavy hydrocarbon oil, sulfur is evolved and becomes a component of the flue gas, requiring removal using appropriate scrubbers. U.S. Pat. Nos. 4,325,817, 4,263,128 describe the use of varied catalysts for absorbing SOx in the oxidizing environment of a regenerator. The catalyst is then transferred to the reducing environment of the reactor where the sulfur is converted to hydrogen sulfide which is then removed from the flue gas using scrubbers. A similar process is disclosed in U.S. Pat. No. 4,980,045, where a reactive alumina catalyst (preferably gamma alumina) is used as the particulate solid, or as a component of the particulate solid within a heavy oil pretreatment process. The reactive alumina is used to absorb gaseous sulfur compounds in flue gasses in the presence of oxygen. U.S. Pat. No. 4,604,268, teaches the removal of hydrogen sulfide within gasses using cerium oxide.
Alternate processes for removal of sulfur from a fluid stream include using zinc oxide silica and a fluorine containing compound as taught in U.S. Pat. No. 5,077,261, or metal silicates as in U.S. Pat. No. 5,102,854, zinc oxide, silica and molybdenum disulfide (U.S. Pat. No. 5,310,717). U.S. Pat. No. 4,661,240 disclose the decreasing of sulfur emissions during coking using calcium.
The present invention is directed to a method for upgrading heavy hydrocarbon feedstocks, for example but not limited to heavy oil or bitumen feedstocks, which utilizes a short residence-time pyrolytic reactor operating under conditions that upgrade the feedstock by cracking and coking reactions. The feedstock used within this process may comprise significant levels of BS&W and still be effectively processed, thereby increasing the efficiency of feedstock handling. The process of the present invention provides for the preparation of a partially upgraded feedstock exhibiting reduced viscosity and increased API gravity. The process described herein selectively removes metals, salts, water, and carbonaceous material referred to as asphaltenes. The process maximizes the liquid yield by minimizing coke and gas production. Furthermore, the liquid product produced by the method of the present invention displays a reduced total acid number (TAN) relative to that of unprocessed hydrocarbon feedstock. The present invention also provides a method for reducing the content of sulfur containing gasses evolved during the course of processing a feedstock.
By reducing the TAN of the product, heavy oil feedstocks having a high TAN, and that otherwise command a reduced market value due to their corrosive properties, command higher market value since they can readily be further processed using known upgrading systems, for example FCC or other catalytic cracking procedures, visbreaking, or hydrocracking and the like. High TAN oils usually contain high levels of naphthenic acids that require dilution prior to processing or refining.
The present invention further provides a method of reducing the hydrogen sulfide content of one, or more than one gas component of a product stream derived from rapid thermal processing of a feedstock oil.
It is an object of the invention to overcome disadvantages of the prior art.
The above object is met by the combinations of features of the main claims, the sub-claims disclose further advantageous embodiments of the invention.